Height-adjusting table header.

ViewController.m

@interface HeaderView : UIView

@end

@implementation HeaderView

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = UIColor.blueColor;
    }
    return self;
}

@end

@interface ViewController () <UITableViewDelegate, UITableViewDataSource, UIScrollViewDelegate>

@property (nonatomic, strong) UITableView *tableView;
@property (nonatomic, strong) HeaderView *headerView;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.tableView = [[UITableView alloc] initWithFrame:self.view.bounds style:UITableViewStyleGrouped];
    self.tableView.autoresizingMask = (UIViewAutoresizingFlexibleWidth |
                                       UIViewAutoresizingFlexibleHeight);
    [self.view addSubview:self.tableView];
    
    self.tableView.dataSource = self;
    self.tableView.delegate = self;
    
    [self.tableView registerClass:UITableViewCell.class forCellReuseIdentifier:@"Cell"];
    
    self.tableView.backgroundView = UIView.new;
    self.headerView = HeaderView.new;
    self.headerView.autoresizingMask = UIViewAutoresizingFlexibleWidth;
    self.headerView.frame = CGRectMake(0, 0, self.view.bounds.size.width, 250);
    [self.tableView.backgroundView addSubview:self.headerView];
    
    self.tableView.contentInset = UIEdgeInsetsMake(CGRectGetHeight(self.headerView.bounds), 0, 0, 0);
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return 100;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"Cell"];
    cell.textLabel.text = [NSString stringWithFormat:@"Cell %ld", indexPath.row];
    return cell;
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    static CGFloat const HeaderMinimumHeight = 44.0;
    
    CGFloat referenceHeight = self.tableView.contentInset.top;
    CGFloat offset = referenceHeight + scrollView.contentOffset.y;
    CGRect headerFrame = self.headerView.frame;
    headerFrame.size.height = MAX(HeaderMinimumHeight, referenceHeight - offset);
    
    self.headerView.frame = headerFrame;
}

@end